When the electromagnetic wave is propagated in the high dielectric constant material, its wavelength can be shortened. By utilizing the theory, the dielectric material can be used to replace the traditional metal material, and under the same index, the volume of the wave filter can be reduced. The research on the dielectric filter is a hot spot of the communication industry all the time. The wave filter is regarded as the important component of the wireless communication products, and the dielectric filter is very important for the miniaturization of the communication products.
Usually the TM (horizontal magnetism) mode dielectric filter is mainly composed of the dielectric resonant column 103, the sealing cover 102, the tuning screw 101, and the metal cavity 104, referring to FIG. 1.
According to the operating principle of the TM mode dielectric resonant cavity, when the dielectric resonator works normally, there is the high electric field distribution in the combining sites of the upper and lower end faces of the dielectric resonant column 103 with the metal cavity 104. If the upper and lower end faces of the dielectric resonant column do not keep in touch with the metal cavity 104 sufficiently, it will cause that the impedance is discontinuous, the field energy cannot be transmitted out, the high dielectric constant and high quality factor of the dielectric cannot be exerted, and even the dielectric will be burn. So, it is particularly crucial whether the upper and lower surfaces of the dielectric resonant column keep in touch with the surfaces of the metal cavity well in the TM mode dielectric filter. How to solve the fixation and contact of the TM mode dielectric resonant column becomes the key research direction of the dielectric filter application.
The dielectric resonator of the related art refers to FIG. 1, wherein the upper surface of the dielectric resonant column 103 is crimped by the sealing cover 102, used for the close contact of the dielectric and the sealing cover 102; and the lower surface of the dielectric resonant column 103 is welded or closely connected to the metal cavity 104 in other ways, used for close contact with the bottom surface of the metal cavity. The sealing cover 102 and the metal cavity 104 are sealed through the screw, to form one closed cavity. Because the temperature coefficient of the dielectric resonant column is different from that of the metal material, once that kind of resonant cavity is influenced by the temperature to swell or shrink, the whole upper surface of the dielectric resonant column will have the interval or be pushed, which influences the performance and service life of the filter seriously.
The solution of the related art is to add the conductive elastomer between the cover and the dielectric resonant column, and that conductive elastomer is used for contacting the cover with the dielectric resonant column. The dielectric filter guarantees the good contact of the dielectric resonant column and the cover by relying on that the conductive elastomer springs back under press. But because the dielectric resonator is only connected by several contacts of the spring, and the contact area and depth of the contacts are not the same when the cavity swells or shrinks with the change of the temperature, thus causing the change of the performance index of the filter.